Processes for extracting aluminum from aluminous ores

ABSTRACT

There are provided processes for extracting aluminum ions from aluminous ores and for preparing alumina. Such processes can be used with various types of aluminous ores such as aluminous ores comprising, for example, various types of metals such as Fe, K, Mg, Na, Ca, Mn, Ba, Zn, Li, Sr, V, Ni, Cr, Pb, Cu, Co, Sb, As, B, Sn, Be, Mo, or mixtures thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.13/662,703 filed on Oct. 29, 2012, that is a continuation of U.S.application Ser. No. 13/471,901 filed on May 15, 2012 (granted as U.S.Pat. No. 8,337,789 on Dec. 25, 2012), that is continuation of U.S.application Ser. No. 12/900,371 filed on Oct. 7, 2010 (granted as U.S.Pat. No. 8,241,594 on Aug. 14, 2012), that is a continuation of U.S.application Ser. No. 12/601,079 filed on Nov. 20, 2009 (granted as U.S.Pat. No. 7,837,961 on Nov. 23, 2010) which is a 35 USC 371 nationalstage entry of PCT/CA2008/000877 filed on May 7, 2008 which claimspriority from U.S. provisional application No. 60/939,254 filed on May21, 2007. These documents are hereby incorporated by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to improvements in the field of chemistryapplied to extraction of aluminum from aluminous ores. For example, suchprocesses are useful for extracting aluminum from aluminous orescomprising various types of metals such as Fe, K, Mg, Na, Ca, Mn, Ba,Zn, Li, Sr, V, Ni, Cr, Pb, Cu, Co, Sb, As, B, Sn, Be, Mo, or mixturesthereof.

BACKGROUND OF THE INVENTION

More than 96% of the alumina which is produced worldwide is obtainedfrom bauxite, which is a mineral that is particularly rich in alumina(40-60%) and whose main suppliers are from Jamaica, Australia, Brazil,Africa and Russia. In certain areas of the world there are largequantities of aluminous ores, which are aluminosilicates (for exampleargillite, nepheline, etc.) that are relatively rich in alumina(20-28%). However such areas have received little attention up to nowbecause the production costs for extracting aluminum from such oresremained too high. In these aluminous materials, and contrary tobauxite, aluminum oxide is associated with silicated or sulfated phases.Thus, the Bayer process cannot be used, which means that alternativetreatments for the production of alumina must be used or developed.Various processes have been proposed so far in order to extract aluminumfrom such aluminous ores comprising aluminosilicates but there is stillroom for improvement or for alternative routes.

SUMMARY OF THE INVENTION

According to one aspect, there is provided a process for extractingaluminum ions from a mixture comprising iron ions and the aluminum ions.The process comprises recovering the aluminum ions from a compositioncomprising the aluminum ions, the iron ions, an organic solvent and anextracting agent adapted to form an organometallic complex substantiallyselectively with the iron ions or with the aluminum ions which issoluble in the organic solvent.

According to one embodiment, the composition can comprise an acidicaqueous phase comprising aluminum ions and an organic phase comprisingiron ions complexed with the extracting agent and wherein the aluminumions are recovered by separating the aqueous phase from the organicphase. The aqueous phase can have a pH of about 1 to about 2.5 or ofabout 2. The extracting agent can be chosen from phosphoric acids andderivatives thereof, and phosphinic acids and derivatives thereof. Forexample, the extracting agent can be chosen from di-2-ethylhexylphosphoric acid (HDEHP), bis(2,4,4-trimethylpentyl) phosphinic acid and2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester. The extractingagent can have a concentration of about 0.5 M to about 1.5 M in theorganic phase or of about 1 M in the organic phase. The composition canhave a volumic ratio organic phase:aqueous phase of about 1:1. Afterextraction (passing the composition through the membrane), the aqueousphase can be separated from the organic phase, and the aluminum ions canrecovered in the aqueous phase and the aqueous phase can be treated witha base (for example NaOH, KOH, or a mixture thereof). The aqueous phasecan be treated with the base so as to obtain a pH of at least about 4.The process can further comprise treating the organic phase with HCl andisolating the iron ions in the form of Fe³⁺.

According to another embodiment, the composition can comprise an acidicaqueous phase comprising iron ions and an organic phase comprisingaluminum ions complexed with the extracting agent, and wherein thealuminum ions are recovered by separating the aqueous phase from theorganic phase. The aqueous phase can have a pH of about 2.5 to about3.5. The extracting agent can be a phosphinic acid or a derivativethereof. For example, the extracting agent can bebis(2,4,4-trimethylpentyl) phosphinic acid. The extracting agent canhave a concentration of about 10% to about 25% v/v with respect to theorganic solvent or of about 20% v/v with respect to the organic solvent.The composition can have a volumic ratio aqueous phase:organic phase ofabout 1:1 to about 1:3. During the process, the composition can be at atemperature of about 30° C. to about 50° C. or at a temperature of about35° C. to about 45° C. After extraction through the membrane, theaqueous phase can be separated from the organic phase. The complexedaluminum ions can be recovered in the organic phase. The organic phasecan then be treated with HCl so as to obtain an aqueous compositioncomprising the aluminum ions.

For example, the organic solvent can be chosen from hydrocarbons. Forexample, the organic solvent can be chosen from C₅-C₁₂ alkanes andmixtures thereof. The organic solvent can also be hexane or heptane. Theorganic phase and the aqueous phase can be separated by means of afiltration membrane, for example a hollow fiber membrane. Such membranecan comprise polypropylene, polyvinylidene difluoride, or a mixturethereof. The aqueous phase can be treated with the base so as to obtaina pH of at least about 4. The process can also further comprise aseparation by filtration so as to obtain Al(OH)₃. The process can alsocomprise washing the Al(OH)₃. The process can also comprise convertingAl(OH)₃ into Al₂O₃. Conversion of Al(OH)₃ into Al₂O₃ can be carried outat a temperature of about 800° C. to about 1200° C.

According to another aspect there is provided a composition comprisingaluminum ions, iron ions, an organic solvent and an extracting agentadapted to form an organometallic complex substantially selectively withthe iron ions or with the aluminum ions which is soluble in the organicsolvent.

According to another aspect, there is provided a composition comprisingan acidic aqueous phase comprising aluminum ions and an organic phasecomprising iron ions complexed with an extracting agent.

According to another aspect, there is provided a composition comprisingan acidic aqueous phase comprising iron ions and an organic phasecomprising aluminum ions complexed with an extracting agent.

The various parameters, embodiments and examples previously describedconcerning the processes can also be applied, when possible, to thesecompositions.

According to another aspect, there is provided a process for at leastpartially separating aluminum ions from iron ions comprised in acomposition, the process comprising substantially selectivelyprecipitating at least a portion of the iron ions in basic conditions inwhich the pH is of at least 10. The iron ions can be precipitated from abasic aqueous composition comprising NaOH or KOH. For example, the basecan be reacted with the composition to obtain a mixture in which the pHis of at least 10, and then, the at least portion of precipitated ironions can be separated from the rest of the mixture. For example, theprecipitated iron ions can be separated from the rest of the mixture bycarrying out a filtration, a decantation, a centrifugation, orcombinations thereof. The process can further comprise rinsing theobtained precipitated iron ions with a basic solution. The basicsolution can have a concentration of about 0.01 M to about 0.02 M. ThepH can be at least 11, at least 12, about 10.8 to about 11.2, about 11.8to about 12.0, between 10 and 11, between 10.5 and 11.0 or about 11.5 toabout 12.5. The process can further comprise purifying the precipitatediron ions by means of a hollow fiber membrane.

According to another aspect, there is provided a process for extractingaluminum from an aluminum ore, the process comprising:

-   -   leaching the aluminum ore with an acid so as to obtain a        leachate and a solid residue;    -   removing at least a portion of iron ions contained in the        leachate by:        -   (i) substantially selectively precipitating the at least            portion of the iron ions in basic conditions in which the pH            is of at least 10, so as to obtain an aluminum enriched            composition; or        -   (ii) substantially selectively complexing the at least            portion of the iron ions with an extracting agent adapted to            form an organometallic complex substantially selectively            with the iron ions so as to obtain an aluminum enriched            composition.

For example, the acid can be HCl. The aluminum ore can leached with HClat a temperature of at least 80° C., at least 90° C., or about 100° C.to about 110° C. HCl can have a concentration of about 6 M. The aluminumore/acid ratio can be about 1/10 in weight by volume.

For example, the removal of the at least portion of iron ions can becarried out by precipitating the iron ions from a basic aqueouscomposition. The composition can comprise comprising NaOH or KOH.

For example, the removal of the at least portion of iron ions can becarried out by reacting the leachate with a base in order to obtain a pHof at least 10 and precipitating the iron ions.

For example, the precipitated iron ions can be separated from the restof the leachate by carrying out a filtration, a decantation, acentrifugation, or mixtures thereof.

The process can further comprise rinsing the obtained precipitated ironions with a basic solution. The basic solution can have a concentrationof about 0.01 M to about 0.02 M. The pH can be at least 11, at least 12,about 10.8 to about 11.2, or about 11.5 to about 12.5. The process canfurther comprise purifying the precipitated iron ions by means of ahollow fiber membrane.

The removal of the at least portion of iron ions can be carried out byreacting the leachate, under acidic conditions, with the extractingagent and an organic solvent in order to obtain a composition comprisingan acidic aqueous phase comprising aluminum ions and an organic phasecomprising iron ions complexed with the extracting agent. The aluminumenriched composition can be obtained by separating the aqueous phasefrom the organic phase. The aqueous phase can have a pH of about 1 toabout 2.5, or about 2. The extracting agent can be chosen fromdi-2-ethylhexyl phosphoric acid (HDEHP), bis(2,4,4-trimethylpentyl)phosphinic acid and 2-ethylhexyl phosphonic acid mono-2-ethylhexylester). The extracting agent can have a concentration of about 0.5 M toabout 1.5 M in the organic phase or about 1 M in the organic phase.

For example, the organic solvent can be chosen from C₅-C₁₂ alkanes andmixtures thereof. The organic solvent can be heptane. The compositioncan have a volumic ratio organic phase:aqueous phase of about 1:1. Theorganic phase and the aqueous phase can be separated by means of afiltration membrane. The membrane can be a hollow fiber membrane. Themembrane can comprise polypropylene, polyvinylidene difluoride, or amixture thereof.

After passing the composition through the membrane, the aqueous phasecan separated from the organic phase. The aluminum ions can be recoveredin the aqueous phase and the aqueous phase is treated with a base (suchas NaOH or KOH). The aqueous phase can be treated with the base so as toobtain a pH of at least about 4. The process can further comprise aseparation by filtration to obtain Al(OH)₃, which can be eventuallywashed.

For example, the aluminum ore can be crushed and roasted before beingleached.

For example, before removal of the iron ions, the leachate is treatedwith a base.

For example, before removal of the iron ions, the leachate can bedistilled so as to reduce its volume.

For example, the process can further comprise at least partiallyrecovering the aluminum ions present in the aluminum enrichedcomposition.

For example, the aluminum enriched composition can be treated with anextracting agent adapted to form an organometallic complex substantiallyselectively with the aluminum ions in the presence of an organic solventand an acid solution in order to form a composition comprising an acidicaqueous phase comprising impurities and an organic phase comprisingaluminum ions complexed with the extracting agent. The aluminum ions canbe recovered by separating the aqueous phase from the organic phase. Forexample, the aqueous phase can have a pH of about 2.5 to about 3.5. Theextracting agent can be a phosphinic acid or a derivative thereof. Theextracting agent can be bis(2,4,4-trimethylpentyl) phosphinic acid. Theextracting agent can have a concentration of about 10% to about 25% v/vor about 20% v/v with respect to the organic solvent. The organicsolvent can be chosen from C₅-C₁₂ alkanes and mixtures thereof. Theorganic solvent can be heptane. The composition can have a volumic ratioaqueous phase:organic phase of about 1:1 to about 1:3. The organic phaseand the aqueous phase can be separated by means of a membrane (forexample a hollow fiber membrane). The membrane can comprisepolypropylene, polyvinylidene difluoride, or a mixture thereof. Thecomposition can be at a temperature of about 30° C. to about 50° C., orabout 35° C. to about 45° C. After passing the composition through themembrane, the aqueous phase can be separated from the organic phase. Thecomplexed aluminum ions can be recovered in the organic phase. Theorganic phase can then be treated with HCl so as to obtain an aqueouscomposition comprising the aluminum ions. The aluminum ions can beconverted into Al(OH)₃ by contacting it with a base. Al(OH)₃ can then beconverted into Al₂O₃. Such a conversion of Al(OH)₃ into Al₂O₃ can becarried out at a temperature of about 800° C. to about 1200° C.

BRIEF DESCRIPTION OF DRAWINGS

In the following drawings, which represent by way of example only,various embodiments of the invention:

FIG. 1 shows a bloc diagram of a process according to one embodiment ofa process for extracting aluminum from an aluminous ore.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

Further features and advantages will become more readily apparent fromthe following description of various embodiments as illustrated by wayof examples only in the appended drawings wherein:

As it can be seen from FIG. 1, such a process can comprise varioussteps, and each of these steps can eventually be individually consideredhas being a process.

Preparation of Argillite Sample

Argillite can be finely crushed in order to help along during thefollowing steps. For example, micronization can shorten the reactiontime by few hours (about 2 to 3 hours). In order to remove most of theiron, a leaching step at room temperature is optionally carried outbetween the crushing step and the roasting step (see option 1). Thisoperation is, for example, carried out with hydrochloric acid HCl (12 M)and an argillite/acid ratio (weight/volume) of 1:5 is used. Depending onexperimental conditions (sizes of the particles, time of treatment,agitation system), about 65% to about 93% of the iron can then beremoved. However, this leaching step can also bring in a certainpercentage of the aluminum (0-5%). The last step of the preparation ofargillite comprises roasting the pretreated argillite. This can beaccomplished at a temperature greater than 550° C. for a period of about1 to 2 hours. For example, a heat treatment makes it possible toincrease the quantity of extracted aluminum by about 30% to about 40%for the same period of time. In others words, the quantity of extractedaluminum is doubled. When leaching at room temperature is carried out, aphase separation before roasting can be made in order to recover theacid and reduce heating costs.

Acid Leaching

Acid leaching comprises reacting the crushed and roasted argillite witha hydrochloric acid solution at elevated temperature during a givenperiod of time. For example, the argillite/acid ratio can be of about of1:10 (weight/volume), the HCl concentration can be of about 6 M, thetemperature can be of about 100° C. to about 110° C., and the reactiontime can be of about 5 to about 7 hours. Under such conditions, morethan about 90% of the aluminum and about 100% of the iron can beextracted in addition to impurities.

During the second half of such a treatment (for example the last 2 or 3hours), a portion of the acid can be recovered by condensation. Once theextraction is terminated, the solid (argillite impoverished in metals)can be separated from the liquid by decantation or by filtration, afterwhich it is washed. The residual leachate and the washing water may becompletely evaporated. The corresponding residue can thereafter bewashed many times with water so as to decrease acidity and to lower thequantities of sodium hydroxide (NaOH) that are required to adjust the pHduring iron removal. Final volume accounts for 10% to 20% of initialvolume. The acid recovered will can be re-utilized after having adjustedits titer either by adding gaseous HCl, or by adding concentrated HCl(12 M). After the reaction, the titer of the acid can vary from about 4M to about 6 M depending on experimental conditions. With respect to thesolid, it represents about 65% to about 75% of the initial mass ofargillite, it can be valorized and be used again either as an ionexchange resin, or as an adsorbent.

Removal of Iron

Removal of iron can be carried out by precipitation of the latter inbasic medium for example at a pH of at least 10 or at a pH of about 11.5to about 12.5. Such a step can be made by adding NaOH, for example at aconcentration of 10 M. Other bases such as KOH can also be used. Then,all that is required is to separate the solid portion from the liquidportion by filtration, decantation or centrifugation and to rinse thesolid by means of a diluted base, such as a solution of NaOH (forexample NaOH at a concentration of 0.01 M to 0.02 M). Then, the solid iswashed with distilled water. The liquid portion comprises aluminum andalkaline-earths. A substantially complete removal of the iron and ofnearly all the impurities (other metals) can thus be achieved.Optionally, it is possible to recover iron by using a refining step byliquid-liquid extraction through a hollow fiber membrane (see option 2).

Alternatively (see option 3), removal of iron can be carried out byusing an extracting agent and a hollow fiber membrane. Variousextracting agents that could substantially selectively complex iron ionsover aluminum ions (or aluminum ions over iron ions) could be used insuch a step depending an Al/Fe ratio. For example, extraction can becarried out by using HDEHP (diethylhexylphosphoric acid) as anextracting agent adapted to complex iron ions. A concentration of about1 M of HDEHP can be used in an organic solvent, such as heptane or anyhydrocarbon solvent. Such an extraction can require relatively shortcontact times (few minutes). For example, the pH of the order of 2 canbe used and aqueous phase/organic phase ratio can be of about 1:1. Itwas observed that is possible to extract from 86% to 98% iron under suchconditions. It will be understood that in the present case, iron istrapped in the organic phase. To recover iron in an aqueous phase, areverse extraction with hydrochloric acid (2 M or 6 M) and organicphase/acidic phase ratio of about 1:0.5 can then be carried out. In sucha case, the resulting aqueous phase is rich in Fe³⁺ ions.

Aluminum Recovery

The solution obtained from the previous step using either theprecipitation or the extraction technique is relatively clean and mainlycontains aluminum for example about 90% to 95% (without thealkaline-earths in the case of precipitation). Recovery of the lattercan be carried out by liquid-liquid extraction for example by using asame hollow fiber membrane and an extracting agent that is adapted tocomplex at least substantially selectively aluminum over other metals orresidues. For example, bis(2,4,4-trimethylpentyl) phosphinic acid (suchas the one sold under the name Cyanex™ 272) can be used as an extractingagent specific to aluminum. For example, this extracting agent can beused at a concentration of about 20% v/v in an organic solvent such asheptane. The ratios between the aqueous phase and the organic phase canbe of about 1:1 to about 1:3. For example, the extraction temperaturescan be of about 40° C. and the pH can be maintained at about 2.5 toabout 3.5. It was observed that such a technique makes it possible toextract more than 70-90% of the aluminum. After the aluminum has beentrapped in the organic phase, it can be recovered in the form of aconcentrate of Al³⁺ ions by using a back extraction. For example, thereverse extraction can be carried out at a temperature of about 40° C.with hydrochloric acid (for example at a concentration of 6 M). Underthis condition, more than 90% of aluminum can be recovered. Then, Al³⁺can be converted into aluminum hydroxide Al(OH)₃ by addition of NaOH.Finally, Al(OH)₃ can be converted into alumina (alumina Al₂O₃) byroasting Al(OH)₃ for example at a temperature of about 800° C. to 1200°C.

The following non-limiting examples further illustrate the invention.

EXAMPLES Example 1 Preparation of Argillite Sample

Crushing of mudstone: The resulting micronization average employed forthe tests ranges between 10 and 50 microns.

Roasting: Crushed mudstone was roasted at least during 1 hour at atemperature of 600° C. Its average composition was:

Al₂O₃ 21.0% Fe₂O₃  8.0% K₂O  1.5% Na₂O  0.9% TiO₂  0.9% CaO 0.08% ZnO0.06% SiO₂ 51.0%

Acid Leaching

500 g of argillite crushed and roasted were added to 5 liters ofhydrochloric acid 6 M. The mixture was then heated at 100° C.-110° C.during 7 hours.

After reaction, the liquid part was separated from the solid part byfiltration. The solid was washed with distilled water which was added tothe liquid portion. This washing makes it possible to recover part ofthe aluminum trapped in the solid. This solid had a dry mass of 345±-5g, which corresponds to a loss of about 30%-32%.

The remaining liquid part, containing aluminum, iron and a great part ofthe impurities initially present in mudstone, was reduced by evaporationat a temperature of 100° C. to 90% of its initial volume. Residualvolume was then 50 mL. The liquid compositions before and afterevaporation were:

Evaporated leaching Leaching solution solution Composition (%)Composition (%) [concentration (mg/L)] [concentration (mg/L)] Aluminum47.63 [9 250] 47.86 [59 500] Iron 31.54 [6 125] 31.07 [38 625]Alkaline-earths 19.30 [3 749] 19.53 [24 277] (Na, Mg, K, Ca) Othermetals  1.53 [297.3] 1.54 [1 920]

All the ions species seem to remain soluble.

Removal of Iron

The residual volume was slightly diluted (+25%) and concentratedhydroxide sodium (10 M) was added until a pH higher than 11.5 wasreached. The formed precipitate was separated from the solution bystandard filtration and was washed several times with NaOH dilued andhot ultra-pure water. The precipitate contained all the iron and themajority of the metal impurities. The filtrate contained in addition toions Al³⁺ mainly alkaline-earths and some following impurities:

Major filtrate impurities (%) Iron 0.14 Sodium 94.13 Alkaline-earths5.71 (Mg, K, Ca) Other metals 0.02Na⁺ came from soda and was also the Al(OH)₄ ⁻ counter-ion.

Aluminum Recovery

The filtrate is adjusted at a pH of 2.5 to 3.5 by addition of HCl 6 M.The resulting solution is extracted by means of the complexing agent,Cyanex 272, at a concentration of 20% volume/volume in an organicsolvent with a volumetric ratio of 1:1. The extraction is carried out ata temperature of 40° C. in a membrane contactor with hollow fibers. Inless than about 30 to 60 min, more than 85% of aluminum is extracted.The pH adjustment is performed by a regulation loop controlling the NaOH(10 M) addition. Complexed Al³⁺ in Cyanex are then recovered by carryingout a back extraction with HCl (6 M) at 40° C. and an organic phase/acidphase volumetric ratio of 1:0.5. After the back extraction, thecomposition of the recovered acid phase is:

Composition (%) Aluminum 92.81 Iron 0 Alkaline-earths 7.14 (Na, Mg, K,Ca) Other metals 0.05

To increase the percentage of purity, the Al³⁺ ions are precipitated inthe form of Al(OH)₃ hydroxide, then washed several times with ultra-purewater. The composition of the hydroxide becomes:

Composition (%) Aluminum 99.09 Iron 0 Alkaline-earths 0.88 (Na, Mg, K,Ca) Other metals 0.03

Further purification can be performed by recrystallization

While a description was made with particular reference to the specificembodiments, it will be understood that numerous modifications theretowill appear to those skilled in the art. Accordingly, the abovedescription and accompanying drawings should be taken as specificexamples and not in a limiting sense.

What is claimed is:
 1. A process for extracting aluminum ions from analuminous ore, said process comprising: leaching said aluminous ore withan acid to obtain a composition comprising aluminum ions and iron ions;at least partially removing said iron ions from said composition bysubstantially selectively precipitating said iron ions at a pH of atleast 10 by reacting said composition with a base and at least partiallyremoving said precipitated iron ions, thereby obtaining an Al-richcomposition comprising Al³⁺ ions; and purifying said Al³⁺ ions.
 2. Theprocess of claim 2, wherein said aluminous ore is leached with HCl at atemperature of at least 100° C.
 3. The process of claim 1, whereinpurifying said Al³⁺ ions comprises reacting said Al³⁺ ions with HCl. 4.The process of claim 3, wherein said pH is between 10 and
 11. 5. Theprocess of claim 1, wherein said Al³⁺ ions are purified by substantiallyselectively precipitating them.
 6. The process of claim 1, wherein saidpH is about 11.5 to about 12.5.
 7. A process for extracting aluminumions from an aluminous ore, said process comprising: leaching saidaluminous ore with HCl to obtain a composition comprising a leachate anda solid residue; separating said leachate and said solid residue fromone another; at least partially removing iron from said leachate bysubstantially selectively precipitating iron ions by reacting saidleachate with a base and removing a so-formed precipitate, to obtain anAl-rich composition comprising Al³⁺ ions; and purifying said Al³⁺ ions.8. The process of claim 7, wherein said Al³⁺ ions are purified bysubstantially selectively precipitating them.
 9. The process of claim 7,wherein said Al³⁺ ions are substantially selectively precipitated byreacting said Al-rich composition with a base.
 10. The process of claim7, wherein said Al³⁺ ions are substantially selectively precipitated byreacting said Al-rich composition with an acid.
 11. The process of claim7, wherein said iron ions are at least partially removed from saidleachate by substantially selectively precipitating them at a pH of atleast
 10. 12. The process of claim 7, wherein said pH is between 10 and11.
 13. The process of claim 7, wherein said pH is at least
 11. 14. Theprocess of claim 7, wherein said pH is about 11.5 to about 12.5.
 15. Aprocess preparing alumina, said process comprising: leaching analuminous ore with HCl to obtain a composition comprising a leachate anda solid residue; separating said leachate and said solid residue fromone another; at least partially removing iron from said leachate bysubstantially selectively precipitating iron ions by reacting saidleachate with a base and removing a so-formed precipitate, to obtain anAl-rich composition comprising Al³⁺ ions; purifying said Al³⁺ ion; andconverting said Al³⁺ ions into alumina.
 16. The process of claim 15,wherein said Al³⁺ ions are substantially selectively precipitated byreacting said Al-rich composition with a base.
 17. The process of claim15, wherein said Al³⁺ ions are substantially selectively precipitated byreacting said Al-rich composition with an acid.
 18. The process of claim15, wherein said iron ions are at least partially removed said leachateby substantially selectively precipitating them at a pH of at least 10.19. The process of claim 15, wherein said pH is between 10 and
 11. 20.The process of claim 15, wherein said pH is about 11.5 to about 12.5.